Cholestatic conditions in which bile duct epithelia (BDE) are the target of disease are collectively known as "cholangiopathies". At present, the only treatment for cholangiopathies, ursodeoxycholic acid, is effective only at improving biochemical markers and delaying liver transplant in patients. No treatment has been directed toward bile ductular proliferation, because the understanding of bile ductular proliferation in health and disease is poorly understood. Recently, we have shown that extracellular nucleotides regulate bile ductular proliferation via P2Y nucleotide receptors, and that blockade of P2Y receptors markedly decreases bile ductular proliferation. These findings have been complemented by findings in other organs, such as the lungs and kidneys. Thus, signaling via extracellular nucleotides is an attractive pharmacologic target for regulation of bile ductular proliferation. Ecto-nucleotidases known as nucleoside triphosphate diphosphohydrolases (NTPDases) are critical regulators of P2Y activation and downstream activity. Recent studies from our laboratory have shown that the ecto-nucleotidase NTPDase2 (CD39L1) is an important regulator of P2Y receptor activation in BDE. NTPDase2 is expressed in a distinct liver fibroblastic cell population within the portal area of the liver known as portal fibroblasts (PF). Preliminary data from our laboratory suggest that NTPDase2 functions to regulate bile ductular proliferation. We propose that NTPDase2 expression in PF attenuates activation of P2Y receptors in BDE linked to bile ductular proliferation and that this regulation is lost in biliary fibrosis. We plan to test this hypothesis through the three following specific aims: (1) Determine how extracellular nucleotides regulate bile ductular proliferation. (2) Define the role of NTPDase2 in the regulation of bile ductular proliferation. (3) Identify factors regulating NTPDase2 expression in normal and diseased liver. We anticipate that the results of these proposed experiments will lead to novel pharmacologic approaches for the regulation of bile ductular proliferation in biliary cirrhosis.